Exhaust nozzle flaps for gas turbine engines are typically cooled by a combination of film and convective cooling, such as shown in U.S. Pat. No. 4,081,137 to Sutton et al. Referring to FIG. 5 of that patent, a convergent/divergent exhaust nozzle is shown, both of which comprise flaps of "double walled" louvered construction. Cooling air is brought into the upstream ends of the convergent flaps and travels downstream between the hot gas path wall and a back wall wherein it convectively cools the hot wall. The cooling air, now somewhat warmer, is dumped into the gas path through slots in the hot wall at various locations along the length of the convergent flaps and film cools downstream portions of the flaps. The film cooling air from the convergent flaps passes into the throat of the divergent nozzle thereby providing additional film cooling of the divergent nozzle flaps. As shown in FIG. 14 of Sutton et al, some of the cooling air flowing within passageways of the divergent nozzle flaps is redirected by suitable duct means into coolant channels within adjacent seal flaps to cool the seal flaps.
One drawback of the cooling concept described in the above-mentioned patent is that the cooling air is coolest when it enters the upstream end of the flaps and becomes hotter as it travels downstream. Yet, the downstream ends of the divergent flaps are the hottest due to lower efficiency cooling. Thus, high temperature gradients may exist from the upstream to downstream ends of the divergent nozzle flaps, particularly during afterburning, creating stresses which can reduce life expectancy of the nozzle.
U.S. Pat. No. 4,203,286 to R. E. Warburton describes another exhaust nozzle cooling arrangement. Referring to FIG. 3 thereof, hollow convergent flaps include coolant channels extending along their length. Coolant enters the channels through inlets in the upstream ends of the flaps, and coolant exits the channels into the gas path through outlets in the downstream ends of the hot inner walls. The coolant leaving these outlets is directed into the throat of a downstream divergent nozzle to film cool the divergent nozzle flaps. Seal flaps disposed between adjacent convergent nozzle flaps may cover the coolant outlets in the convergent flaps depending upon the position of the nozzle. The outlets are uncovered when the nozzle is in its maximum open position to permit maximum coolant flow to the divergent nozzle. As the convergent nozzle closes, the seals cover more and more of the coolant outlets to reduce the coolant flow to the divergent nozzle.
U.S. Pat. No. 4,098,076 to J. H. Young et al describes a single flap two dimensional exhaust nozzle wherein coolant air from upstream (either ram air or fan air) is brought into the upstream ends of compartments within hollow flaps. The cooling air passes through various pressure reducer valves and is directed into various compartments (at different pressures for pressure balancing) within the nozzle flap. The reduced pressure cooling air in at least one compartment is redirected upstream between the double walls of a gas path face sheet, and is ejected into the gas path through a slot to film cool the flap, as shown in FIG. 3 thereof.
Of general interest as regards the state of the art of cooling nozzle flaps and seals is U.S. Pat. No. 4,171,093 to F. L. Honeycutt, Jr. et al.